Friction-Harvesting Generators Could Lead to Self-Powered Touchscreens

Researchers at Georgia Tech have developed nanoscale triboelectric generators, or generators that harvest energy from the friction of two different materials rubbing together. These tiny generators could have a host of applications from powering small sensors or, because they are transparent, creating self-powered touchscreen displays.

"The fact that an electric charge can be produced through this principle is well known," said Zhong Lin Wang, a Regents professor in the School of Materials Science and Engineering at the Georgia Tech. "What we have introduced is a gap separation technique that produces a voltage drop, which leads to a current flow, allowing the charge to be used. This generator can convert random mechanical energy from our environment into electric energy."

The triboelectric generator operates when a sheet of polyester rubs against a sheet made of polydimethysiloxane (PDMS). The polyester tends to donate electrons, while the PDMS accepts electrons. Immediately after the polymer surfaces rub together, they are mechanically separated, creating an air gap that isolates the charge on the PDMS surface and forms a dipole moment.

If an electrical load is then connected between the two surfaces, a small current will flow to equalize the charge potential. By continuously rubbing the surfaces together and then quickly separating them, the generator can provide a small alternating current. An external deformation is used to press the surfaces together and slide them to create the rubbing motion.

The researchers found that creating patterns on one of the surfaces really boosted electrical output. They tried lines, cubes and pyramids and found pyramids to be best, generating as much as 18 volts at about 0.13 microamps per square centimeter. The patterns were created using a silicon mold and the researchers say the entire production process for the generators is simple, affordable and easy to scale up.

Beyond just energy-harvesting touchscreens for our gadgets, the researchers also see them acting as self-powered pressure sensors. The generators produce a current from the lightest touch so even a feather or water droplet would register as contact.

The generators have proven they work well and consistently. They were able to keep producing an electrical current through over 100,000 cycles and after days of use. So now, the researchers are working on building a system that includes energy storage to make them even more useful.